Transcript
Professor Cam Nelson
Limestone is sedimentary rock, so it must have formed at the Earth’s surface.
It starts off as sediment, and it must have more than 50% calcium carbonate in it to qualify as limestone. Rock such as mudstone or sandstone – where the grains have come down rivers and been delivered to the sea – they can have a highish calcium carbonate content perhaps as well, but less than 50%, and so we could call those calcareous mudstones or calcareous sandstones to indicate that carbonate content.
So limestone specifically must have more than 50% calcium carbonate, and the little grains that give you that calcium carbonate are typically the smashed up shell remains of a whole variety of organisms. These can be molluscs, gastropods, echinoderms, bryozoans, brachiopods, worm tubes – most invertebrate animals secrete some type of skeleton, and very often that’s a calcium carbonate skeleton.
So in New Zealand, they are the main contributors to the formation of carbonate sediments, which, once they are changed into rock, become limestones.
Acknowledgements:
McDonald’s Lime Limited
Dr Roger Grace
National Institute of Water and Atmospheric Research (NIWA)
Ken-ichi Ueda
